Two Cumbria police staff suspended last month, after details of their chauffeur-driven police and crime commissioner's travel expenses were leaked to the media, have been cleared of any wrongdoing and will return to work.

A 47-year-old man who was arrested on 10 April on suspicion of data protection offences and misconduct in public office will face no criminal action and has had his suspension lifted.

Another staff member, a man aged 59 who was interviewed by police on a voluntary basis, will also face no criminal action and will return to work.

Two other people – a 50-year-old woman who works for Cumbria constabulary and a 54-year-old man from Penrith who does not work for the force – remain under investigation by the force's professional standards department. Their bail dates have been extended to 5 July and the constabulary is preparing files for the Crown Prosecution Service.

The investigation was launched after a whistleblower claimed that Richard Rhodes, Cumbria's Conservative police and crime commissioner (PCC), had used taxpayers' money to pay for chauffeur-driven vehicles – only paying the money back when details appeared in the press.

Rhodes was criticised earlier this month by Cumbria's crime panel for being unclear and inconsistent over the expenses, which amounted to £700 for two trips to evening engagements.

Rhodes told the panel: "I had been uncomfortable about the cost that had been incurred from the moment I became aware about it. I had been considering repaying the cost, but there had been no imperative to make the decision quickly."

The suspensions within Cumbria police prompted concern from MPs and others concerned with freedom of information, and led to questions being asked in parliament about the treatment of whistleblowers.

Tim Farron, the president of the Liberal Democrats and MP for Westmorland and Lonsdale, said on Thursday that the force's decision to lift suspensions on the two staff was long overdue and called on the police to drop any charges on the final two people currently on bail.

"Whistleblowers need to be protected and not prosecuted. It is welcome news that two staff will not face charges," he said. "But a further two are still on bail. Arresting people for doing a public service and releasing this information is deeply worrying and the charges against the two remaining staff should be dropped."

Rhodes said: "This is an active police investigation and I am not at liberty to answer any questions at this stage owing to the risk of prejudicing an ongoing police investigation.

"As outlined in the Policing Protocol Order 2011 the chief constable remains operationally independent to the police and crime commissioner. I have no authority to influence an active police investigation.

"The chief constable has the responsibility of the day-to-day management and decisions of staff employed by Cumbria constabulary."

Theresa May, the home secretary, told the home affairs select committee in April that she would look into claims that legitimate whistleblowers were being targeted, but stressed that PCCs were ultimately accountable to the electorate and the public would decide if they had done their job properly.

Committee member David Winnick asked May: "Do you accept in some instances police and crime commissioners have given the impression that they're on a spending spree and really enjoying themselves?"

May said she did not accept that, adding: "The whole point is the PCCs will be accountable to their electorate."

A statement by Cumbria police on Thursday said the force's "staff and police officers have a duty to protect and manage the information they have privileged access to.

"The constabulary has well established internal whistleblowing procedures for issues to be raised by officers and staff and dealt with in a proper manner. This investigation continues to look at any alleged unlawful disclosure of information from the constabulary, to ensure our communities can have trust and confidence in the way we deliver policing in the county."